The present invention pertains to the indicator art and, more particularly, to a means for indicating slight movements of a mechanical member.
The prior art is replete with mechanical indicating systems. Patents have issued for systems indicating that a booth is occupied, a fish is on a line, a water skier has fallen and so forth. However, none of the prior art mechanical indicating systems has provided a solution to a particular problem, an example of which is found in the aircraft art.
In commercial aviation transports, the flaps are deployed as a result of a torque being coupled to a gear box. The torque is normally supplied from a drive motor which is capable of driving a number of gear boxes. If one of the flaps should become jammed, as by icing or any one of numerous other causes, the force coupled to it could easily damage the flap and, possibly, a significant portion of the wing surface. To prevent such damage, the prior art has provided a device known as a torque limiter between the torque source and the gear box. In operation, the torque limiter couples the torque from the source through an input cam plate, series of steel balls and an output cam plate to the gear box. Each steel ball is located between input and output cam plates and rides in a dished cutout of the latter. If the torque required to rotate the output cam plate exceeds a predetermined value, the steel balls ride up onto the ridge portion of the dished cutouts. This results in a force which drives the output cam plate away from the input cam plate causing brake disks mounted thereon to forcibly engage stator disks which are coupled through the torque limiter housing to the aircraft main frame. Thus, torque from the torque source is effectively grounded and destructive forces are deflected from reaching the jammed flap.
During the course of a flight, one or more flaps may fail to be deployed in response to a pilots command. Not uncommonly, once the aircraft lands the flaps are operating properly and, as such, it is difficult if not impossible for the ground crew to identify the source of the problem. That is, it is not known whether the failure for the flaps to respond was a result of an intermittent drive motor, a linkage problem, failure of the gear box or jamming of the flaps, i.e. a failure upstream or downstream of the torque limiter.
As a diagnostic aid it would be useful to know whether or not during the flight the torque limiter was tripped. If it was, this is an indication that the failure occurred downstream from the torque limiter, i.e. at the gear box, flap or linkage therebetween. Thus, it would be desirable to provide a torque limiter trip indicator which would indicate to the ground crew whether or not torque limiter tripping had occurred.
The constraints imposed on such a torque limiter indicator are both numerous and stringent. Such an indicator must mount to an existing torque limiter without extensive limiter modification. Further, since there is only slight relative movement of limiter parts during its transition to and from the limiting action mode, an indicator must be capable of providing a positive, reliable limiter trip indication in response to very slight mechanical movements. In addition, the trip indicator must provide permanent witness to the condition of torque limiting even though the torque in the system may thereafter return to a normal condition. Beyond this, the limiter must be capable of being reset, as by the ground crew.